This invention relates to methods for making electronic devices, and more particularly, to methods for making sensors for use in detecting magnetically encoded information in magnetic storage media.
Devices utilizing giant magnetoresistance (GMR) effects have utility as magnetic sensors, especially in read heads used in magnetic disc storage systems. The GMR effect is observed in thin, electrically conductive multi-layer systems having magnetic layers. Magnetic sensors utilizing the GMR effect are frequently referred to as xe2x80x9cspin valvexe2x80x9d sensors.
A spin valve sensor is typically a sandwiched structure including two ferromagnetic layers separated by a thin non-ferromagnetic layer. One of the ferromagnetic layers is called the xe2x80x9cpinned layerxe2x80x9d because it is magnetically pinned or oriented in a fixed and unchanging direction. A common method of maintaining the magnetic orientation of the pinned layer is through anti-ferromagnetic exchange coupling utilizing a proximate, i.e. adjacent or nearby, anti-ferromagnetic layer, commonly referred to as the xe2x80x9cpinning layer.xe2x80x9d The other ferromagnetic layer is called the xe2x80x9cfreexe2x80x9d or xe2x80x9cunpinnedxe2x80x9d layer because its magnetization can rotate in response to the presence of external magnetic fields.
The benefits of spin valve sensors result from a large difference in electrical conductivity exhibited by the devices depending on the relative alignment between the magnetizations of the GMR element ferromagnetic layers. In order for antiferromagnetically pinned spin valve sensors to function effectively, a sufficient pinning field from the pinning layer is required to keep the pinned ferromagnetic layer""s magnetization unchanged during operation. Various anti-ferromagnetic materials, such as NiMn, FeMn, NiO, IrMn, PtPdMn, CrMnPt, RuRhMn, and TbCo, have been used or proposed as antiferromagnetic pinning layers for spin valve sensors. GMR sensors can be used to sense information encoded in magnetic storage media. In operation, a sense current is passed through a GMR stack. The presence of a magnetic field in the storage media adjacent to the sensor changes the resistance of a GMR stack. A resulting change in voltage drop across the GMR stack due to the change of the resistance of the GMR stack can be measured and used to recover magnetically stored information.
These sensors typically comprise a stack of thin sheets of a ferromagnetic alloy, such as NiFe (Permalloy), magnetized along an axis of low coercivity. The sheets are usually mounted in the head so that their magnetic axes are transverse to the direction of disc rotation and parallel to the plane of the disc. The magnetic flux from the disc causes rotation of the magnetization vector in at least one of the sheets, which in turn causes a change in resistivity of the stack.
The output voltage is affected by various characteristics of the sensor. The sense current can flow through the stack in a direction that is perpendicular to the planes of the stack strips, i.e. current-perpendicular-to-plane or CPP, or the sense current can flow through the stack in a direction that is parallel to the planes of the stack strips, i.e. current-in-plane or CIP. The CPP operating mode can result in higher output voltage than the CIP operating mode. Higher output voltages permit greater precision and sensitivity of the read sensor in sensing magnetic fields from the magnetic medium. Therefore, it is desirable to maximize the output voltage of the read sensor.
In an effort to achieve greater magnetic storage capacity, the size of magnetic recording heads is continually being reduced. The lithographic process of lift-off has been a standard process in magnetic recording head fabrication for many years.
The standard lift-off process as used to define the stripe width in an abutted junction magnetic recording head includes the following steps. First a spin valve film stack is deposited on a layer of material commonly referred to as a first half gap. A dual layer resist is applied to the film. The bottom layer of the resist is undercut with respect to the top layer of the resist. Ion milling is used to remove the spin-valve film stack that is not protected by the dual layer resist, down to the first half gap material. Ion beam deposition can be used to deposit a layer of permanent magnet and lead material over the surface of the first half gap and the dual layer resist. Because the bottom layer of the resist is undercut with respect to the top layer, the permanent magnet and lead material does not coat the sides of the bottom layer of the resist. Thus the sides of the bottom layer of the resist and the overhang of the top layer of the resist are exposed so that solvents can be used to attack the resist layers and lift-off the permanent magnet and lead material that coats the dual layer resist above the spin valve film stack.
A dual layer resist process for use in making magnetic recording heads is disclosed in U.S. Pat. No. 5,669,133, the disclosure of which is hereby incorporated by reference. A dual layer resist technique has been used in the past because material deposited after the resist will coat the sidewalls of the resist. Without the dual layer undercut, solvents could not penetrate the material on the sidewalls of the resist to dissolve the resist.
Problems arise when one attempts to extend the dual layer process to very small dimensions. The undercut needs to be big enough to form an area where no permanent magnet and lead material metal is deposited, so that the resist stripper can make contact with the bottom resist layer to dissolve it. With very narrow structures, this undercut can become a significant portion of the total width of the resist structure. This causes the resist structure to become unstable and fall over. Complicating this even more is that the rate at which the bottom layer undercuts the top layer is not perfectly controllable. Even when the structure would be stable if the correct undercut amount is achieved, the non-uniformity of the process would make it unsuitable for manufacturing.
There is a need for a magnetic recording head fabrication process that does not require the use of a dual layer resist.
This invention provides a method for making a magnetic sensor for a disk drive read head, the method comprising the steps of depositing a magnetoresistive stack on a surface of a first layer of material, depositing a resist layer on a first portion of the magnetoresistive stack, removing a second portion of the magnetoresistive stack not covered by the resist layer, depositing a layer of additional material on the magnetoresistive stack, the resist material, and the surface of the first layer, removing the additional material from sidewalls of the resist material, and using a lift-off process to remove the resist material. Magnetic sensors made by the above method are also included.
More generally, the invention provides a method for making a semiconductor device, the method comprising the steps of depositing a layer of first material on a surface of substrate, depositing a resist layer on a first portion of the first material, removing a second portion of the layer of the first material not covered by the resist layer, depositing a layer of additional material on the first material, the resist layer, and the surface of the substrate, removing the additional material from sidewalls of the resist layer, and using a lift-off process to remove the resist layer. Semiconductor devices made by the above method are also included.